Renewable energy systems, such as wind turbine systems, solar power systems, energy storage systems, etc., have increasingly been used for power generation throughout the world. Renewable energy systems can include a plant or farm having a plurality of power generation units (e.g. wind turbines) that are collectively coupled to a utility grid at a point of interconnect. The renewable energy system can include a control system having a farm level controller(s) and unit level controller(s) to regulate the real and reactive power output of the renewable energy system.
A renewable energy farm may be required to fulfill a reactive power capability at the point of interconnect to provide a desired power factor (e.g. based on a power factor setting). In some cases, renewable energy systems may be required to have the capability to provide a rated reactive power capability in a voltage range of ±10% of nominal voltage at the point of interconnect. To fulfill this requirement, an on-load tap changing transformer can be required. Including an on-load tap changing transformer at each power generation unit (e.g. each wind turbine) can be costly. As an alternative, reactive power capability can be provided by adjusting active power production of the renewable energy farm at certain voltage levels (e.g. voltage levels outside of the ±5% of nominal voltage band). However, this can require knowledge of the actual reactive power limits of the renewable energy farm.
The reactive power limit of a renewable energy farm is typically determined by aggregating the reactive power limits of individual power generation units in the farm. The reactive power limit of an individual power generation unit is typically defined as rated reactive power for the unit and does not change based on system behavior. In situations wherein individual power generation units are clamped to voltage limits, the individual power generation units may not be able to provide rated reactive power, thus the rate reactive power is not a good estimate of the actual reactive power limit of the power generation unit.
Thus, a need exists for determining actual reactive power limits of a renewable energy farm under various system conditions. A system and method that can reduce active power production based on the actual reactive power capability in order to meet a power factor requirement would be particularly useful.